CreateUIDefinition.json

{
  "handler": "Microsoft.Compute.VmExtension",
  "version": "0.0.1-preview",
  "parameters": {
    "elements": [
    ],
    "outputs": {
      "vmName": "[vmName()]",
      "location": "[location()]"
    }
  }
}

CreateUIDefinition2.json

{
  "handler": "Microsoft.Compute.VmExtension",
  "version": "0.0.1-preview",
  "parameters": {
    "elements": [
      {
        "name": "fileUris",
        "type": "Microsoft.Common.FileUpload",
        "label": "Script files",
        "toolTip": "The script files that will be downloaded to the virtual machine.",
        "constraints": {
          "required": false
        },
        "options": {
          "multiple": true,
          "uploadMode": "url"
        }
      },
      {
        "name": "commandToExecute",
        "type": "Microsoft.Common.TextBox",
        "label": "Command",
        "defaultValue": "powershell.exe -ExecutionPolicy Unrestricted -Command .\\Script1.ps1",
        "toolTip": "The command to execute, for example: powershell.exe -ExecutionPolicy Unrestricted -Command .\\Script.ps1 -Arg1 'foo' -Arg2 'bar'",
        "constraints": {
          "required": true
        }
      }
    ],
    "outputs": {
      "vmName": "[vmName()]",
      "location": "[location()]",
      "fileUris": "[elements('fileUris')]",
      "commandToExecute": "[elements('commandToExecute')]"
    }
  }
}